Groundwater intrusion through a building's foundation can cause serious damage. In addition to increased concrete deterioration and accelerated rebar corrosion, basement dampness can ruin expensive electrical and mechanical equipment, which is often located in basement space, and can increase maintenance requirements through frequent repainting or cleaning to combat mold growth. Furthermore, the intruding water raise the interior relative humidity thereby accelerating the corrosion rate of mechanical equipment in the area and creating unacceptable air quality and concomitant health problems due to the rapid growth of bacteria and mold.
In selective problem areas, the usual approach to the treatment of water intrusion problems is to ‘trench and drain’. In other words, to excavate and expose the wall area and the base of the foundation, to replace waterproofing on the wall surface, and to install a drain tile system around the building or affected area. Other areas, such as floors, are untreatable using conventional methods.
Electro-osmosis has origins in 1809, when F. F. Reuss originally described an experiment that showed that water could be forced to flow through a clay-water system when an external electric field was applied to the soil. Research since then has shown that flow is initiated by the movement of cations present in the pore fluid of clay, or similar porous medium such as concrete, brick, and cementitious construction materials; and the water surrounding the cations moves with them. The basic physics and chemistry of electro-osmosis can be found in several textbooks and treatises. Glasstone, S., Textbook of Physical Chemistry, 2d ed., D. Van Nostrand Company, Inc., Princeton, N.J., 1946. Tikhomolova, K. P., Electro-Osmosis, Ellis Horwood Limited, Chichester, West Sussex, England, 1993.
Electro-osmosis is typically used to solve the problem of groundwater intrusion, which can cause serious damage to a building's foundation and interiors. As noted above, basement dampness, can ruin expensive electrical and mechanical equipment, which is often located in basement space; can increase maintenance requirements through frequent repainting or cleaning to combat mold growth; and can make affected areas uninhabitable or even unusable due to poor air quality. Electro-Osmotic Pulse (EOP) technology typically offers an alternative that can mitigate some water-related problems from the interior of affected areas without the cost of excavation. Examples of such systems are described below.
In one system, humidity is removed from a damp structure by positioning electrodes within the structure and applying a D.C. voltage across them. U.S. Pat. No. 3,856,646, Methods and Electrodes for the Drying of Damp Buildings, to Morarau, Dec. 24, 1974.
In another system, chloride ions are removed from concrete by embedding an anode in an electrolyte and establishing an electric current between the anode and the concrete structure in order to avoid corrosion of the concrete's reinforcing means, typically steel rebar. U.S. Pat. No. 5,296,120, Apparatus for the Removal of Chloride from Reinforced Concrete Structures, to Bennett et al., Mar. 22, 1994.
Another system discloses a process for changing the bond strength between concrete and its steel reinforcement by passing DC current through the concrete. U.S. Pat. No. 5,312,526, Method for Increasing or Decreasing Bond Strength Between Concrete and Embedded Steel, and for Sealing the Concrete-to-Steel Interface, to Miller, May 17, 1994.
Still another method used to eliminate humidity from concrete uses electro-osmosis to pass current pulses in a predetermined pattern through the concrete. U.S. Pat. No. 5,368,709, Method and Apparatus for Controlling the Relative Humidity in Concrete and Masonry Structures, to Utklev, Nov. 29, 1994.
A method that claims improvement over existing methods by choice of a narrow range of relationships among the three pulse durations of the pulse train provides longer anode life while optimizing the process of dehydration. U.S. Pat. No. 5,755,945, Method for Dehydrating Capillary Materials, to Kristiansen, May 26, 1998.
An improvement over previous methods claims to increase anode life while optimizing dehydration and the time to effect it. It uses a specific pulse train in which the positive pulse width is much greater than the negative pulse width that is, in turn, greater than the off period. U.S. Pat. No. 6,117,295, Method for Dehydrating a Porous Material, to Bjerke, Sep. 12, 2000.
A method that claims to be an improvement over the '709 patent provides a control unit to control the pulse width of individual pulses by monitoring characteristics of the energizing source. U.S. Pat. No. 6,126,802, Method and Device for Regulating and Optimizing Transport of Humidity by Means of Electroosmosis, to Utklev, Oct. 3, 2000.
A more recent patent proposes a solution to overcome the disadvantage of the '709 patent when used to dehumidify steel-reinforced structures. It specifically prevents the deterioration of the reinforcing steel by providing a second voltage to the reinforcement steel in addition to the typical electro-osmosis configuration of the '709 patent and its predecessors. U.S. Pat. No. 6,370,643 B1, Method for Effecting Fluid Flow in Porous Materials, to Finnebriaten, Aug. 7, 2001.
An Electro-Osmotic Pulse (EOP) system is realized by installing anodes (positive electrodes) in the interior wall, floor or ceiling of the structure and cathodes (negative electrodes) in the soil exterior to the structure. Due to the extreme electrochemical environment surrounding the anode, special material and geometry requirements may be placed on an anode intended to be used for other than “trickle current” loads or extended periods, or both.
Durable, dimensionally stable anodes are a recent development in anode technology. They have excellent characteristics to include: low resistivity, very low dissolution rates, long life, durability, and corrosion resistance. Durable, dimensionally stable anodes are also referred to as semiconductive anodes. Durable anodes that are classified as dimensionally stable generally consist of a valve metal substrate such as niobium, tantalum, titanium or alloys thereof, with a catalytic coating consisting of precious metal(s), most often from the platinum metal group, and often in oxide form in combination with valve metal oxides as a mixed metal oxide.
Although conventionally used for “humidity control,” a rather unconventional use for EOP systems in porous structures lies in taking water (moisture) removal to extremes, i.e., removing sufficient water to weaken the structure in that a minimum amount of moisture is needed to hold together the porous structure. For example, concrete deteriorates rapidly when significant moisture is removed.
Conventionally, several methods are used to demolish concrete or other masonry structures. Some require a mechanical device or explosives to remove the concrete or masonry material or to dismantle the structure. Most if not all of these processes are noisy, dusty and potentially dangerous to the workers involved.
In a preferred embodiment of the present invention, an objective heretofore undesired in prior patents is attained, i.e., concrete or masonry is treated by electro-osmosis until the concrete or masonry and the structure it is supporting is weakened.